Cathode surface area effect

In this equation, we have set i = /a,i/Ai and icji = /c.ipAii- It follows that in a corrosion cell, the rate of corrosion of the anode is the higher the smaller its surface area is with respect to that of the cathode surface area effect). 

The sputtering rate does not change much with the increase of cathode surface area at low system pressure p= lOmtorr). The plasma treatment is localized and effectively confined. However, at a relatively high system pressure (/) = SOmtorr), the sputtering rate is almost zero for the larger cathode. This case reiterates the importance of system pressure in AMT Ar sputtering treatment. 

FIGU RE 12.26 Effects of both the environmental relative humidity (a) and the nature of the particle (h and c) on the extent of the cathodic surface area. 

Copper Corrosion Inhibitors. The most effective corrosion inhibitors for copper and its alloys are the aromatic triazoles, such as benzotriazole (BZT) and tolyltriazole (TTA). These compounds bond direcdy with cuprous oxide (CU2O) at the metal surface, forming a "chemisorbed" film. The plane of the triazole Hes parallel to the metal surface, thus each molecule covers a relatively large surface area. The exact mechanism of inhibition is unknown. Various studies indicate anodic inhibition, cathodic inhibition, or a combination of the two. Other studies indicate the formation of an insulating layer between the water surface and the metal surface. A recent study supports the idea of an electronic stabilization mechanism. The protective cuprous oxide layer is prevented from oxidizing to the nonprotective cupric oxide. This is an anodic mechanism. However, the triazole film exhibits some cathodic properties as well. 

Figure 20-9 shows the negative effect of uninsulated heating elements on corrosion protection. In a 250-liter tank, an electric tube heating element with a 0.05-m surface area was screwed into the upper third without electrical separation, and in the lower third a tinned copper tube heat exchanger with a 0.61 -m surface area was built in. The Cu heat exchanger was short-circuited for measurements, as required. For cathodic protection, a potential-controlled protection system with impressed current anodes was installed between the two heating elements. The measurements were carried out with two different samples of water with different conductivities. 

A similar effect can be produced if a crevice is present in the steel, since the geometry of the system is such that whereas oxygen can diffuse readily to the metal surface outside the crevice it can only gain access to the metal within the crevice through its very narrow mouth (Fig. 1 A6d), and the large cathode anode area ratio leads to localised attack of the metal within the crevice. 

However, when the amount of added particles increased(W=2.0 or 3.0wt.%), the effective surface area of cathode plate decreased due to the considerable increase of solid holdup between the two electrodes, thus, the amount of copper recovery decreased. In this experimental conditions, the distance between the two electrodes(LAc) also influenced the recovery of copper, as can be seen in Fig. 7. In this figure, the value of R was maximum when the distance(LAc) was 1.5cm, in all the cases studied. 

The surface of the base metal is anodically polarized under the effect of local cells. For a graphical analysis of the phenomena, one must construct the polarization curves for the partial currents at the base metal as well as the overall anodic 4 vs. E curve reflecting the effective rate of dissolution of this metal under anodic polarization. The rate of the cathodic process, 4, at the inclusions is described by the corresponding cathodic polarization curve (since the surface areas of anodic and cathodic segments differ substantially, currents rather than current densities must be employed here). At open circuit the two rates are identical. 

Electrolytic recovery (ER) is the oldest metal recovery technique. Metal ions are plated-out of solution electrochemically by reduction at the cathode.34 There are essentially two types of cathodes used for this purpose a conventional metal cathode and a high surface area cathode (HSAC). Both cathodes can effectively plate-out metals, such as gold, zinc, cadmium, copper, and nickel.22... 

In addition to the use of composite anodes and cathodes, another commonly used approach to increase the total reaction surface area in SOFC electrodes is to manipulate the particle size distribution of the feedstock materials used to produce the electrodes to create a finer structure in the resulting electrode after consolidation. Various powder production and processing methods have been examined to manipulate the feedstock particle size distribution for the fabrication of SOFCs and their effects on fuel cell performance have also been studied. The effects of other process parameters, such as sintering temperature, on the final microstructural size features in the electrodes have also been examined extensively. 

In addition to the criticisms from Anderman, a further challenge to the application of SPEs comes from their interfacial contact with the electrode materials, which presents a far more severe problem to the ion transport than the bulk ion conduction does. In liquid electrolytes, the electrodes are well wetted and soaked, so that the electrode/electrolyte interface is well extended into the porosity structure of the electrode hence, the ion path is little affected by the tortuosity of the electrode materials. However, the solid nature of the polymer would make it impossible to fill these voids with SPEs that would have been accessible to the liquid electrolytes, even if the polymer film is cast on the electrode surface from a solution. Hence, the actual area of the interface could be close to the geometric area of the electrode, that is, only a fraction of the actual surface area. The high interfacial impedance frequently encountered in the electrochemical characterization of SPEs should originate at least partially from this reduced surface contact between electrode and electrolyte. Since the porous structure is present in both electrodes in a lithium ion cell, the effect of interfacial impedances associated with SPEs would become more pronounced as compared with the case of lithium cells in which only the cathode material is porous. 

The effect was more pronounced at the starting potential than at the finish potential. Leidheiser suggested that the best performance is obtained when the cathode/anode surface area ratio is the same as the uncoated metal. Inadequate performance is obtained when the cathode/anode area ratio becomes larger. Qur work agrees with Leidheiser s hypothesis. The B210/GBL coatings have rest potentials less noble than the B40 coated steel panels and perform best in the salt fog environment. 

The major factors probably responsible for the acceleration effect of additives are (1) the charge density of the electron system of the additive and (2) the exchange of electrons between electrode, 7r-bonded additive molecule, and the complexed metal ions in the solution. Inhibition effect and cathodic passivation are explained in terms of blocking of the catalytic surface, which results in a decrease in the available surface area (45). 

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